Automatic motor-starting rheostat.



No. 779,875. PATENTED JAN. 10, 1905. E. SOHA-TTNER & O. D. HASKINS.

AUTOMATIC MOTOR STARTING RHEOSTAT.

APPLICATION FILED MAY 13. 1904.

14 @vs RC' O Wifnesws. invenfors.

g5 ERNEST SCHATTNER, X CARYL l1 HASKINSV 57 W 72w TY.

UNITED STATES Patented January 10, 1905.

PATENT OFFIC ERNEST SCHATTNER AND OARYL D. HASKINS, OF SOHENEOTADY, NETVYORK, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORA- TION OF NE YORK.

AUTOMATIC MOTOR-STARTING RHEOSTAT.

SPECIFICATION forming part of Letters Patent No. 779,875, dated January10, 1905.

Application filed May 13, 190 Serial No. 207,745.

To all whom it may concern:

Be it known that we, ERNEST SCHATTNER, a subject of the King of GreatBritain, and (JARYL D. HAsKINs, a citizen of the United States, bothresiding at Schenectady, in the county of Schenectady and State of NewYork, have invented certain new and useful Improvements in AutomaticMotor-Starting Rheostats, of which the following is a specification.

This invention relates to controllers for electric motors, andparticularly to that type of controllers known as automaticmotor-starting rheostats. Its object is to provide such a rheostat bywhich a smooth resistance gradient will be obtained, and we accomplishthis by employing a self-reducing resistancethat is, a resistance theohmic value of which is decreased by the passage of the current throughit.

Prior to our invention the common practice has been to providemotor-starting rheostats with wire resistances connected to studsarranged in an arc of a circle and a pivoted switch-arm cooperating withthe studs. With such a device the resistance is cut into and out of themotor-circuit in steps. Obviously a starting-rheostat with which asmooth resistance gradient is obtained would give more satisfactoryresults. It has long been known that certain substances possess anegative temperature coefficient of resistancethat is, they decrease inohmic value when heated and such substances have been termedself-reducing resistance. Some substances possess this characteristic tosuch an extent that they may be used in place of hand-operatedresistances in electric circuits where it is desirable that theresistance be great when the current is first applied and shall then begradually re duced. Among such substances magnetite possesses thisself-reducing characteristic to a marked degree and is thus particularlywell suited for use as starting resistance for elec tric motors and forsimilar purposes. In a pending application filed by E. Schattner March31, 1904:, and serially numbered 200, 881, is described a self-reducingresistance unit having magnetite and a silicate mixed in properproportions and held in a tube under pressure.

This invention relates to a motor-starting rheostat employing such aself-reducing resistance and arranged so that it can be operatedautomatically from a distance. As the ohmic value of the self-reducingresistance decreases gradually as the material is heated by the passageof the current through it,'no electrically-actuated moving parts arenecessary to vary the resistance in the motor-circuit; but in order thatthe resistance material may cool, and thus be in readiness to againproperly start the motor whenever that is desired, we provide means bywhich the resistance is automatically short-circuited as soon as themotor is up to speed.

Our invention further comprises means whereby the resistance isautomatically shortcircuited when the counter electromotive force of themotor rises sufiiciently to permit connecting the motor directly acrossthe lines without danger of injury to the coils of the motorarmature.

The novel features of our invention will be definitely indicated in theclaims appended hereto.

The details of construction and the mode of operation of our improvedautomatic motorstarting rheostat will be better understood by referenceto the following description, taken in connection with the accompanyingdrawing, which shows a plan view of the preferred embodiment of ourinvention.

In the drawing, 1 indicatesa base-plate, of soapstone or similarinsulating material. provided with openings therein by which it may bemounted upon a support in a vertical position. Mounted on the base-plateis a self-reducing resistance 2, preferably consisting of one or moreunits constructed as described in the application above referred to.Also mounted on the base-plate is a differential relay having coils 3and 4 wound on suitable cores, which are connected at one end by an ironbridgepiece 5. On the other end of each core is a airgap, as shown.

at one end on the bridge-piece 5, and its other end is adapted to movebetween the pole-pieces 6 and 7, pins 9, of brass or other non-magneticmaterial, being provided in the ends of the pole-pieces 6 and 7 toprevent the armature from sticking thereto. A switch-blade 10 is securedto armature 8, and a switch-clip 11 is mounted on the base-plate inposition to be engaged by the switch-blade 10 when armature 8 is drawnto its uppermost position. A binding-post 12 is mounted on thebase-plate and connected by a flexible conductor 13 to the switch-blade10. Also mounted on the baseplate are the binding-posts 14, 15, and 16.A line-switch 17 and automatic circuit-breaker 18 are connected in thesupply-mains leading to the motor at any convenient point, which may beat a distance from the motor. One of the lines is connected to thebinding-post 1 1 and the other to the field 19 and armature 20 of themotor; The other side of the field is connected to binding-post 1 1 andthe other side of the armature to the binding-post 16. Post 16 isconnected to one side of the selfreducing resistance 2, a knife-switch21 being inserted in this connection, if desired, and the other side ofthe resistance is connected to post let. Binding-post 12 and the clip 11are also connected to opposite sides of the resistance 2, so that whenthe switch-blade 10 engages clip 11 the resistance 2 is shortcircuited.The coil 3 of the relay is connected between the posts and 16, which areconnected to opposite sides of the motor-armature. The coil 4; of therelay is connected between posts 14L and 15 and is therefore across thelines.

As thus constructed the operation of the rheostat is as follows: Thearmature 8 normally rests by gravity against the pin 9 in the pole-piece7. To start the motor, the lineswitch 17 and circuit-breaker 18 at thedistant point are closed, thus closing circuit through the coil 4 of therelay, through the motor-field 19, and through the armature and theselfreducing resistance 2 in series. As the coil 4c of the relay isacross the lines, the current pole-piece 7. The ohmic value of theself-reducing resistance 2 is relatively high when circuit is firstclosed, so that only a small current is admitted to the motor-armature.The material, however, is heated by the passage of the current throughit, and hence its resistance steadily decreases, and the substanceswhich constitute the resistance material may be so proportioned that theohmic value of the resistance falls in direct proportion to the rise inthe counter electromotive force of the motor. The drop in voltage acrossthe motorarmature when circuit is first closed is very small, so thatonly a very small current flows through coil 3 of the relay; but as themotor comes up to speed the counter electromotive force of the motor andhence the drop in voltage across the armature rise, so that more andmore current passes through coil When the motor reaches normal speed,the current in the coil 3 of the relay is so great that its magnetizingeffect is suflicient to overcome that of coil L, and armature 8 is drawnup against the pin in pole-piece 6, thus moving the switchblade 10 intoengaging relation to the contact 11 and short-eircuiting the resistance2. It will thus be seen that the motor is brought up to speed merely bythe closure of a switch at a distant point, that the resistance 2prevents dangerous overloading ol the motor while coming up to speed,that the resistance is short-circuited when .the motor is running atnormal speed in order that it may cool, and thus be ready for arepetition of the operation, and that this short-circuiting of theresistance is dependent entirely upon the counter electromotive force ofthe motor, so that the resistance cannot be short-circuited until themotor has reached its proper speed. \Vhen the line-switch 17 or thecircuit-breaker 18 is opened, all circuits are opened, and the armature8 falls by gravity against the pin in the pole-piece 7, thus restoringall parts to their original positions.

\Ve have illustrated and described herein the form of our inventionwhich we prefer to use; but we do not wish to be understood as limitedin any way to this specific device, as many modifications can be madetherein which We consider within the scope of our invention and which weaim to cover in the claims appended hereto.

Vhat we claim as new, and desire to secure by Letters Patent of theUnited States, is

1. The combination of an electric motor, a self-reducing resistance,means distant therefrom for closing circuit through the motorarmatureand the resistance in series, and automatic means for short-circuitingthe resistance.

2. The combination of an electric motor, a selt'reducing resistance,means distant therefrom for closing circuit through the motorarmatureand the resistance in series, and automatic means for short-circuitingthe resistance when its ohmic value has fallen to a predeterminedamount.

3. A starting-rheostat having a self-red ucing resistance, means forclosing circuit through the motor-armature and the resistance in series,and means dependent upon the counter electromotive'force of the motorfor shortcir euiting the resistance.

4. A starting-rheostat having a self-reducing resistance, means forclosing circuit to the motor through the resistance, a relay having anarmature, and means whereby said armature when attracted short-circuitsthe resistance.

5. An automatic starting-rheostat having a self-reducing resistance,means for closing circuit to the motor-armature through the resistance,an electromagnet having its coil connected across the motor-armature, anarmature for said electromagnet, and means whereby said armature whenattracted short-circuits the resistance.

6. An automatic starting-rheostat having a self-reducing resistance,means for closing circuit through the motor-armature and the resistancein series, a differential relay having one coil connected across themotor-armature and the other across the lines, an armature for saidrelay, and means whereby said armature short-circuits the resistance.

7. An automatic starting-rheostat having a self-reducing resistance,means for closing the circuit through the motor-field, and through themotor-armature and the self-reducing resistance in series, adifferential relay having one coil connected across the motor-armatureand the other across the lines, a pivoted armature for said relay, astationary contact, and a contact carried by said pivoted armaturecooperating with said stationary contact in one position toshort-circuit the selfreducing resistance.

In Witness whereof we have hereunto set our hands this 12th day of May,1904.

ERNEST SCHATTNER. CARYL D. HASKINS.

Witnesses:

BENJAMIN B. HULL, V HELEN ORFORD.

